Stream: helpdesk (published)

Topic: When should I read config file?

Andrey Oskin (Feb 22 2022 at 09:10):

I can't quite understand difference between __init__ function and regular code written in module.

So, the problem is the following: I want to store some configuration parameters in a toml file, somewhere in a file system, and I want to read it during using step. Where should I put initialization steps?

Version №1

module Foo
using TOML
const OPTIONS = Ref(0)

OPTIONS[] = TOML.parsefile("/config.toml")["var"]

end #module

or Version №2

module Foo
using TOML
const OPTIONS = Ref(0)

function __init__()
  OPTIONS[] = TOML.parsefile("/config.toml")["var"]
  return
end

end #module

Which one is a correct way of initializing variables?

Andrey Oskin (Feb 22 2022 at 09:14):

And second question, is there any common Julia path, where I can keep this configuration file? I can do it in ~/.config/... but I would prefer something more system independent.

jar (Feb 22 2022 at 09:20):

Idk if there's a julia version of appdirs but I think that's the platform-agnostic application-agnostic answer to "which directory". Julia itself should use the XDG dirs too but currently doesn't.

Fredrik Ekre (Feb 22 2022 at 09:20):

The first will run when precompiling the package, the second when using the package.

Fredrik Ekre (Feb 22 2022 at 09:22):

Andrey Oskin said:

And second question, is there any common Julia path, where I can keep this configuration file? I can do it in ~/.config/... but I would prefer something more system independent.

Maybe have a look at https://github.com/JuliaPackaging/Preferences.jl

Andrey Oskin (Feb 22 2022 at 09:38):

Thank you, so I suppose I need second, if I want to change settings between runs.

Fredrik Ekre (Feb 22 2022 at 09:39):

Between restarts, yes.

Andrey Oskin (Feb 22 2022 at 09:45):

Thank you.

I do not quite get the idea of Preferences.jl. It can store preferences in LocalPreferences.toml file of the package. But packages usually have path ~/.julia/packages/Foo/<some random token>/... where random token is different between package versions. So what, each time I get a new version of the file, my LocalPreferences will be forgotten? It doesn't look convinient.

Fredrik Ekre (Feb 22 2022 at 09:46):

No that is not how it works, the LocalPreferences.toml file is stored in your current project, for example:

$ ls
LocalPreferences.toml  Manifest.toml  Project.toml

$ cat Project.toml
[deps]
Example = "7876af07-990d-54b4-ab0e-23690620f79a"

$ cat LocalPreferences.toml
[Example]
foo = "bar"

Andrey Oskin (Feb 22 2022 at 09:49):

And global in Project.toml of the package?

Yeah, it's not what I really want. I am always running julia with julia --project=. so each time I have isolated environment.

Fredrik Ekre (Feb 22 2022 at 09:50):

It is exactly what you want, if you run julia --project=. it will pick up preferences from the LocalPreferences.toml file next to your Project.toml.

Andrey Oskin (Feb 22 2022 at 09:50):

But thank you, this package gave me few good ideas.

Andrey Oskin (Feb 22 2022 at 09:54):

I guess in my case, I can do the same as thing as PyCall:

const prefsfile = joinpath(first(DEPOT_PATH), "prefs", "Foo.toml")
mkpath(dirname(prefsfile))

Fredrik Ekre (Feb 22 2022 at 09:56):

PyCall.jl is moving to Preferences.jl too (https://github.com/JuliaPy/PyCall.jl/pull/945). I don't understand why Preferences.jl is not exactly what you want?

Last updated: Oct 02 2023 at 04:34 UTC